Microwave phase shifter



May 15, 1956 w. slcHAK MICROWAVE PHASE SHIFTER Filed oct. 2. 1951,United States Patent @hice 2,746,018 atented May 15, 1956 MICROWAVEPHASE SHIFTER William Sichak, Lyndhurst, N. J., assigner, by mesneassignments, to the United States of America as represented by theSecretary of the Navy Application October 2, 1951, Serial No. 249,363

3 Claims. (Cl. S33-29) This invention relates to microwave phaseShifters and more specifically to high speed continuous rotary waveguidephase Shifters.

Waveguide phase shifters are needed in certain microwave systems,generally for shifting the angular position of an antenna beam.Heretofore, various means and methods of shifting the phase of an outputwave with respect tothe input wave have been proposed. The majority ofsuch means are primarily voltage devices with the disadvantage that theoutput power transmitted to the load Vmust he kept very small so as notto disturb the phase relations in the circuit. However, one phaseshifter has been proposed heretofore to transmit relatively largeamounts of power to a load, but this device is not satisfactory forcertain applications becausevof its large physical size andextremefrequency sensitivity.

One of the objects of this invention, therefore, is to provide awaveguide phase shifter of relatively small physical dimensions which iscapable of relatively high power transmission.

Another object of this invention is to provide a waveguide phase shifterwith relatively broad frequency response and substantially linearlyphase shift.

A further object of this invention is to provide a waveguide phaseshifter which is capable of transmitting relatively large amounts ofpower to a load with a minimum lof loss.

Briefly, a phase shifter according to this invention may comprise asection of a circular waveguide with means, such as a helical antenna,for radiating a circularly polarized wave therethrough and receivingmeans which may also comprise ahelical antenna to receive the wave atthe output end of the waveguide section. One or the other or both of theantennas may be caused to rotate about a longitudinal axis, whereby thedegree of phase shift may be controlled, since the phase shift of theoutput voltage is directly proportional to the relative angular'motionof the antennas.

The above-mentioned and other features and objects of this inventionwill become more apparent by reference to the following descriptiontaken in conjunction with the accompanying drawings, wherein:

Fig. l is a longitudinal cross-sectional view of an embodiment of thisinvention;

Fig. 2 is a longitudinal cross-sectional View of another embodiment ofthis invention;

Fig. 3 is a schematic illustration of an embodiment of this inventioncapable of wide shifts in phase; and

Fig. 4 is a schematic illustration of a further embodiment of theinvention.

Referring to Fig. 1 of the drawing, a source of microwave energy isapplied to the phase shifter therein shown through a coaxialconnector 1. The outer conductor 1a of the coaxial connector is joinedto one end of a section of circular waveguide 2. The inner conductor 3of the coaxial connector is coupled to a sleeve 3a which supports arotatable shaft 4 by means of a pair of bearings 5. The sleeve 3asurrounds in spaced relation a sleeve 6 carried by shaft 4 wherebymicrowave energy is coupled through an R. F. choke, formed between thesleeves 3a and 6 and between sleeve 6 and shaft 4, and thus to thewinding 7 of the input antenna 8. The input antenna is mounted on therotating shaft 4 and is a circularly polarized, end radiating. helix,adapted to launch a wave for propagation along the circular waveguide 2in accordance with the H11 mode. The waveguide 2 is dimensioned belowcutot for all higher modes. Another circularly polarized helix 9 woundin the same sense as the input antenna acts as an antenna to receive theradiations emitted by said input antenna 8.

The phase of the output voltage of a circularly polarized antennareceiving a circularly polarized wave launched by a circularly polarizedantenna is directly proportional to the angle of rotation of one antennaabout its longitudinal axis relative to the other antenna. The outputamplitude will be equal to the input amplitude and there will be nophase shift errors, if the ends are perfectly matched and the axialratios of the helices are unitary.

The dimensions and location of each helix S and 9 with respect to theend of the waveguide 2 are so selected as to obtain a polarization asnearly circular as possible and a good impedance match to the coaxialline. One form of helix, which has been found satisfactory forfrequencies near 9375 mc. using a 50 ohm coaxial transmission line forinput and output connections, is a helix composed of a dielectric form10, such as Tel-lon, 0.3 inch in diameter, 11A; inches long with aflange l1 which is W16 of an inch wide by .475 inch in diameter, theliange end of the form having a hole 0.12 inch in diameter and X32 inchdeep in its center to which the Shaft 4 is connected, while the otherend has a hole 0.155 inch in diameter by 15/16 inch deep, the flangebeing bisected by a slot 0.032 Vinch wide and 5A@ inch deep, along oneof its diameters. The winding 7 is laid in semicircular channels cut inthe form 0.031 inch in diameter, consist of 31/2 turns of 0.025 copperwire vstarting 1A; of an inch above the flange and connected to theshaft 4 on which the form l0 is mounted. The Windngs should be fixedfirmly, but not necessarily flush with the surface. A sheath i2 made ofa dielectric, such as Teflon, and is 1% linches long by 0.4 inch inoutside diameter and having a wall thickness of 0.1 inch, ts over thewinding to prevent its displacement when the antenna is rotated at highspeeds. The receiving antenna 9 is substantially identical with theinput antenna 3 except that for 1 inch of dielectric form thereof outfrom the flange, the wall thickness is 0.2 inch. The receiving helix 9is connected to the spring nger contact i3 of an output connector. Theouter conductor 14 of said output connector is connected to thewaveguide 2.

The helicesof the two antennas have a spacing of one inch between theirends. Less spacing would result in direct coupling between the ends, andtherefore, present large errors.

The bearing, motor drive, and helix mounting methods are important forhigh rotational speeds. Irregular bearing surfaces result in physicalunbalance, motor overload, and sudden speed changes, all of which causephase errors. The motor drive must be constant, because a small speeddrift of the driving mechanism results in large phase shift errors athigh rotational speeds. lf the helix mounting is not accurate, theneccentricity errors will be introduced.

In operation, a wave is applied from the coaxial line through coupler 1and choke 6 to the helical antenna 8. The antenna radiates the wave,circularly polarized, axially along the waveguide section 2 and isreceived by the helical antenna 9 for propagation over a coaxial linecoupled at 13, 14. The antenna 9 is maintained fixed while the antenna 8is rotated by shaft 4. By controlling the rotation of the antenna 8 aphase advance or retardation is obtainable.

Where the waveguide 2 is made of a solid cylindrical wall, asubstantially linearly phase shift is obtained cxcept for two pointsV180 apart in the angularsetting of the phase shifter. Thisdiscontinuity at these two points is relatively sharply dened and wasdiscovered to be caused by a resonance of the circular polarization H11mode which occurs in the opposite sense to the main or desiredcircularly polarized H11 mode for which the unit is designed. This sharpdiscontinuity, while not troublesome for many phase shift uses, may besubstantially eliminated by suppression. While different ararngementsmay be provided for effecting this suppression, such as using impedancegrids, the preferred means of suppression comprises the location of oneor more helical slots in the wall of the cylinder forming the waveguide.The angle of the slot depends upon the R. F. frequency and the diameterof the waveguide.

From a consideration of the iields for a circularly polarized H11 modepropagating in a circular waveguide, it may be shown that the resultantH field spirals down the guide in the direction of propagation. gb, theangle this ield makes with the axis of propagation is given by kc p-arctan *1.84m v where +45 is measured counterclockwise from the axis,

, c=cutoff wavelength of H11 mode in,

tg=guide wavelength of circular waveguide.

The wall currents flow at right angles to the H eld and spiral aroundthe inner surface of the waveguide observing the same screw sense as thelaunching helices. Waves of the opposite sense form the angle with theguide axis.

when }\c=1.49" Ag=2.35

= 19 and the current i90+19=109, or -71.

For the opposite sense, =l9 and the current flow angle is i90-l9={71, or-l09.

In Fig. l one such slot is shown at 2a, the spiral of the slot havingthe same sense of direction as the spiral of the helix 7. By thusarranging the slot 2a to parallel the currents resulting from themagnetic eld of the desired H11 mode, the slot intercepts the currentsresulting from the magnetic field of the undesired H11 mode and radiatesthe energy thereof. In certain instances, it is preferable to suppressthis radiation. This suppression of radiation is accomplished by eitheroverlapping the slot 2a with a layer of lossy conductive material 2b orby filling the slot with the lossy conductive material as shown at 2c,in Fig. 2. The lossy conductive material may comprise any materialhaving the desired lossy characteristic, one such material being adielectric containing distributed particles of carbon. The phase shifterprovided with a suppression slot as indicated in 2a lowers sharply the Qof the undesired resonance thus substantially eliminating thediscontinuity observed with a solid Wall cylindrical waveguide.

Another embodiment of this invention as shown in Fig. 2, has a differentdrive arrangement to reduce eccentricity errors and certain motor drivediculties. The coaxial input line 15 is terminated in an open circuitcdquarter wave choke 16 which includes a short circular waveguidedirnensioned far below cutoff for all modes higher than the H11 mode.The inner conductor is terminated Vat 17 in telescoped relation with asleeve conductor 18 which is connected to the helical conductor of theantenna unit 19. The antenna unit 19 is constructed similarly as shownin detail for antenna 9 in Fig. l, the antenna being supported by theend member 20 which in turn is carried by the waveguide section 21. Theantenna 19 proow angle is trudes into the waveguide section in spacedrelation to a receiving antenna 22 Which protrudes through an end member23 carried by the other endof the wave guide section 21. The two endmembers 20 and 23 are supported by bearings 24 and 25 in the couplingunits 26 and 27. The antenna 22 is supported by a conductor 28 which iscoupled to the helical conductor of antenna 22 in iixed relationcoaxially of the coupling member 27. The outer conductor 29 of theoutput connection is coupled to the member 27 with the inner conductor30 secured to the conductor 28. The cylindrical wall of the waveguide 21is provided with a slot 21a similarly as in the case of Waveguide 2,Fig.v 1. The slot 21a is loaded with lossy conductive material 2c.

The end member 2t) is provided with gear teeth 31 whereby the waveguidesection 21 together with antenna 19 can be rotated. By controlling therotation of the waveguide section and the antenna 19, the desired phaseshift is obtained.

In Fig. 3 an embodiment is shown comprising a waveguide section 32containing in the ends thereof an input antenna 33 and an output antenna34. The two antennas are connected to motors 35 and 36, respectively, sothat both antennas may be rotated simultaneously and the direction andspeed of rotation controlled. The input and output connections 37 and 38are coupled to the antennas. If the two antennas 33 and 34 are rotatedin opposite directions, the phase shift can be doubled. The cylinder ofwaveguide 32 is shown provided with two helical slots 32a and 32b. Itshould be understood that more than one or two slots may be used in thewall of the waveguide employed in practicing the invention.

In Fig. 4, a phase shifter similar to the one in Fig. l is shown coupledat the input and output thereof by rectangular waveguides 39 and 40,respectively. 'Ihe lead 7a to antenna 8 is extended into the waveguide39 to pick up the input energy, the lead being connected to a dielectricshaft 41 driven by motor 42 whereby rotation of input antenna 8 iscontrolled. The output end 43 of antenna 9 is likewise disposed inwaveguide 40 for launching R. F. energy in waveguide 40.

While I have described above the principles of my invention inconnection with specific apparatus, vit is to be clearly understood thatthis description is made by way of example only and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

I claim:

1. A phase shifter comprising a circular waveguide section, a helicalinput antenna element for radiating a circularly polarized wave at oneend of said section for propagation therethrough, a helical outputantenna element to receive said wave at the other end of said section,the circular waveguide section dening a path for the energy radiatedfrom said input antenna to said output antenna, means to rotate one ofsaid helical elements relative to the other helical element whereby thephase of the output voltage with respect to the input voltage isproportional to the relative angle of rotation of said elements, meansfor coupling a source of radio frequency energy to said input antenna,said helical input antenna being adapted to launch a wave circularlypolarized with one sense of rotation, said waveguide section includingmeans for suppressing propagation of waves circularly polarized in asense of rotation opposite to said one sense of yrotation including atleast a slot in the wall of said section disposed substantially parallelto electric currents produced in response to the propagation of a Wavecircularly polarized with said given sense of rotation and having lossyconductive material disposed relative to said slot such as to absorbenergy radiated by said slot, whereby relatively large amounts of powermay be transmitted to a load with a minimum of loss.

2. A phase shifter comprising a circular waveguide Ana circularlypolarized wave at one end of said section for propagation therethrough,a helical output antenna element to receive said wave at the other endof said section, the circular waveguide section defining a path for theenergy radiated from said input antenna to said output antenna, means torotate one of said helical elements relative to the other helicalelement whereby the phase of the output voltage with respect to theinput voltage is proportional to the relative angle of rotation of saidelements, means for coupling a source of radio frequency energy to saidinput antenna, said coupling means having a radio frequency chokedisposed at least in part between the fixed and moving parts of thephase shifter, the means for rotating one of said elements includingmeans for rotating said waveguide section, said helical input antennabeing adapted to launch a wave circularly polarized with one sense ofrotation, said waveguide section including means for suppressingpropagation of waves circularly polarized in a sense of rotationopposite to said one sense of rotation including at least one slot inthe wall of said section disposed substantially parallel to electriccurrents produced in response to the propagation of a wave circularlypolarized with said given sense of rotation and having lossy conductivematerial disposed within and along said slot to absorb energy radiatedby said slot, each of said antennas comprising a cylindrical member ofdielectric material and a helical conductor supported thereby, saidradio frequency energy source coupling means comprising a coaxial inputconnector for radio frequency energy, a coaxial output connector, saidcircularly polarized helical input antenna being coupled to the innerconductor of said input connector, said circularly polarized helicalreceiving antenna being coupled to the inner conductor of said outputconnector, means rotatably coupling said circular waveguide section tothe outer conductors of said input and output connectors, said means forrotatably coupling said section including a pair of members havingbearings supporting the ends of said sections, thereby permittingrelatively large amounts oi electromagnetic energy to be transmittedthrough a load with a minimum of loss.

3. A phase shifter comprising a circular waveguide section, a helicalinput antenna element for radiating a circularly polarized wave at oneend of said section for propagation therethrough, a helical outputantenna element to receive said wave at the other end of said section,the circular waveguide section defining a path for the energy radiatedfrom said input antenna to said output antenna, means to rotate one ofsaid helical elements relative to the other helical element whereby thephase of the output voltage with respect to the input voltage isproportional to the relative angle of rotation of said elements, meansfor coupling a source of radio frequency energy to said input antenna,said coupling means having a radio frequency choke disposed at least inpart between the xed and moving parts of the phase shifter, said helicalinput antenna being adapted to launch a wave circularly polarized withone sense of rotation, said waveguide section including means forsuppressing propagation of waves circularly polarized in a sense ofrotation opposite to said one sense of rotation including at least aslot in the wall of said section helically disposed in the same rotarysense as the helical conductors of said antennas, said slots havinglossy conductive material disposed therealong to absorb energy radiatedby said slots, each of said antennas comprising a cylindrical member ofdieelectric material and a helical conductor supported thereby, acoaxial connector having an outer conductor joined to one end of thesection of circular waveguide, and having an inner conductor, arotatable shaft, a sleeve supporting said rotatable shaft, the innerconductor of the coaxial connector being coupled to said sleeve, asecond sleeve surrounded by said iirst sleeve, said second sleeve beingcarried by said shaft whereby microwave energy may be coupled through aradio frequency choke, said radio frequency choke being formed betweenthe rst sleeve and the second sleeve and between the second sleeve andthe shaft, and thus to the winding of the input antenna, said inputantenna being mounted on said rotating shaft, said input antenna beingan end radiating helix adapted to launch a wave for propagation alongthe circular waveguide in accordance with the H11 mode, said waveguidebeing dimensioned below cutoff for all higher modes, each of said helixantennas being so dimensioned and so located as to obtain as nearcircular polarization as possible and to obtain a good impedance matchto the coaxial line, an output coaxial line connector having an outerconductor and an inner conductor, said output conductor being connectedto said waveguide, said output connector having a spring iinger Contactconnected to said receiving helix antenna, the helices of the twoantennas being spaced an amount to at least minimize direct couplingbetween the ends so as to eliminate possibility of large errors.

References Cited in the iile of this patent UNITED STATES PATENTS2,129,712 Southworth Sept. 13, 1938 2,151,118 King Mar. 21, 19392,513,205 Roberts June 27, 1950 2,530,818 FOX Nov. 2l, 1950 OTHERREFERENCES Publication I, Microwave Transmission Circuits, by Ragan,volume 9 of Radiation Laboratory Series, published by McGraw-Hill in1948; pages 375 and 446 relied on. (Copy in Division 69.)

Publication II, Helical Beam Antennas for Wide- Band Applications, byKraus, Proceedings of I. R. E, volume 36, No. 10, October 1948; pages1236-1242.

